1. Field of the Invention
The present invention relates to decorating apparatus for decorating an object, particularly, a circular object, and in a particular application, for decorating a can, and particularly to a digital can decorating apparatus for digitally controlled printing on two-piece cans. Although the disclosure herein describes the invention as applied to decoration of cans, the invention is applicable to decorating any object, and particularly a generally cylindrical or round object which is adapted to be supported, and particularly rotated, in opposition to a digitally controlled printing head.
2. The Prior Art
Conventionally, two-piece cans are decorated by offset printing. In such a process each color ink is contained in a separate inking station that transfers the ink to a blanket. These inks are then simultaneously applied from the blanket to the can in register. If a different image is desired to be printed or a change is desired in the image, it is necessary to completely change the printing plate on which the image is fixed. During changing of the ink colors, the ink distribution rolls must be cleaned to avoid contamination of the new color by the previous color. A representation of such a known device is shown in FIG. 1.
Further examples of such, or similar, can printing devices are known from U.S. Pat. Nos. 3,766,851, 5,799,574 and 6,367,380. U.S. Pat. No. 5,799,574 discloses a relatively high speed apparatus for applying decorations to the exterior of cylindrical containers while they are mounted on mandrels which are disposed along a periphery of a large continuously rotating disk-carrier. Decorations are applied to the containers as they engage a rotating blanket of a decorator that is adjacent the periphery of the carrier. During engagement between the containers and the blanket the containers track the blanket surface through the printing region where the containers and the blanket surface are engaged. This type of decorating equipment includes a number of relatively heavy elements that move at high speed. Because there must be precise coordination between the various elements, inertia forces, lubrication and operating power are significant engineering design considerations, as are equipment down time, maintenance, cost and setup procedures.
Although these prior art devices are functional, they are mechanically quite complex and contain a large number of components which must be controlled during printing and maintained so as to provide images that are uniform in appearance from one can to the next.
Digital printing is used in many environments. Digital printing might be broadly defined as printing without use of printing plates. An example of digital printing is inkjet printing, of which there are several different techniques including the use of a piezo element to apply pressure to a nozzle chamber to force a drop of ink onto a medium, continuous ink supply with required ink droplets channeled onto the medium, thermal printing where a gas bubble in a nozzle chamber creates pressure forcing an ink droplet onto the medium, or ink in solid form is melted as needed and then applied like a liquid ink jet. Ink might be sprayed by a spray jet. Other non-plate techniques of applying ink include thermal wax or resin tracer, dye sublimation, etc. Use of a particular technique of digital printing is not required for performance of the present invention. Inkjet printing overrides the various steps and apparatus associated with producing and mounting and setting plates. With respect to the use of digital printing in can decoration, the additional need for a blanket wheel for cooperating with inkers is avoided.
Apparatus for adapting digital printing technique to decorating of cans or container, and of the type of the present invention, has not previously been disclosed.
Accordingly, it is an object of the present invention to provide an apparatus for a non-contact printing of images on objects, particularly round objects, more particularly cans and specifically two-piece cans, which apparatus, relative to the prior art, is mechanically simple and without a large number of parts. Decoration of cans is described herein as one application of the apparatus. Pursuant to this object, and others which will become apparent hereafter, the present invention provides apparatus for digitally controlled printing directly on the objects or two-piece cans without the need for an intermediate printing blanket.
The inventive apparatus includes means for digitally and electronically controlling the timing and configuration of a printed image on a can surface. Such digitally controlled means may include any known type of non-contact print-head, such as an ink jet print-head. Furthermore, the inventive apparatus includes means for transporting the cans in an indexed fashion in front of or opposed to the print-heads and for rotating the cans in registered alignment from one print-head to the next.
Each of the print-heads is preferably operative to print a single color ink.
Each can is held on a rotatable turret by a respective one of a plurality of mandrels supported on the turret. Each mandrel is driven to rotate on its own axis by a respective servo motor. Each can to be printed is mounted on a respective one of the mandrels. The servo motors rotate and register the mandrels, with the cans mounted thereon, in front of the print-heads which print a respective part of the entire image that is to be printed on the cans.
The mandrel turret is rotated by an indexing drive, such as a servo motor, so that the mandrels follow a circular movement as the turret rotates and so that each mandrel with a can thereon pauses in front of each print-head for a period of time sufficient to permit digitally controlled printing on the can and rotation of the servo motor for registering the can to the image being printed. The turret is mounted to its servo motor by a support shaft. The servo motor and the support shaft are mounted on a main support, such as a Rutherford decorator support, which is in turn mounted on a machine base.
A valve arrangement provided on the support shaft and the turret connect supplies of vacuum and/or of compressed air to each of the mandrels for initially holding and thereafter releasing the cans on the mandrels.
A computer controls the indexed rotation of the turret as well as the rotation and, registering of the cans in front of the print-heads. Digital control of the individual print-heads may also be by the same computer. This computer control allows tremendous flexibility in the control of the printing apparatus itself as well as in the ability to instantaneously change the image being printed.
An additional support is provided for holding the print-heads so that they are directed toward the mandrels mounted on the turret as the mandrels move along the circular path of movement.
In another embodiment of the invention, two groups of print-heads are provided on the additional support. One group of print-heads is arranged on a circular arc having a radius smaller than the radius of the circular path of movement of the mandrels while the other group of print-heads is arranged on a circular arc having a radius larger than the radius of the circular path of movement of the mandrels. In this way the mandrels, together with the cans mounted thereon, are rotated on the turret between the two groups of print-heads. Each print-head in one group is positioned to oppose, i.e. on the same radius as, a respective print-head of the other group so that the cans are printed on from opposite directions as they pass between the print-heads.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described therein.